The present invention relates to a king pin assembly, and more particularly relates to an adjustable assembly for the king pin which releasably mates with a fifth wheel assembly on a tractor-trailer arrangement.
Most large lumber and commercial trucks consist of tractor units and various forms of trailers attached to the tractors. The tractor consists of an engine, cab for the driver, transmission and drive wheels, and a "fifth wheel" which is a horizontal, flat circle of metal with a pie-shaped wedge cut out of its rear-most portion. A downward pointing pin at the front of a trailer slips into the fifth wheel through the pie-shaped opening, and slips down into a retaining hole centred within the fifth wheel. The fifth wheel then bears the pulling load of the tractor and, as the trailer pin is cylindrical in shape, it allows the tractor to hinge at the pin-fifth wheel connection for turns.
Conventionally fifth wheels may be longitudinally adjustable on the tractor unit by means of, for example, an air pressured power pin mounted on the fifth wheel that fits into various slots on the deck of the tractor, allowing the fifth wheel to be moved forwards and backwards. An example of such a construction is shown in Canadian Pat. No. 624,175 of Buvelot issued July 18, 1961.
Several advantages arise if the king pin can be provided with a measure of longitudinal adjustment. For example, this would allow the driver of the vehicle to change the weights on the driving axles of the tractor and the forward-most set of wheels on the trailer, such that he might increase traction on the drive wheels when necessary. As well, relative adjustment of the location of the king pin in the longitudinal direction would permit the driver to adjust the load on the trailer so that all of the axles on the tractor and trailer are of legal weight, rather than one being over legal weight and requiring either special permits or the payment of fines if no permit is available or if the weight is in excess of the permit.
Canadian Pat. No. 355,915 of Gurton issued Feb. 11, 1936 describes and illustrates a relatively simple form of longitudinally adjustable king pin arrangement, in which the king pin is attached to a longitudinally movable thrust bar, which is spring biased to return to starting position after, for example, the tractor and trailer have completed a turn.
Canadian Pat. No. 707,653 of Gravelle issued April 13, 1965 describes and illustrates a king pin mounting which is longitudinally adjustable, in which the king pin depends from a plate which is slidably, longitudinally adjustable. The plate is provided with upwardly directed locking pins which are receivable within several orifices longitudinally aligned in a removable keeper plate overlying this king pin plate. Adjustment of the positioning of the king pin must be done manually with this construction.
It is an object of the present invention to provide an alternative construction of longitudinally adjustable king pin assembly for cooperating with fifth wheel mechanisms. It is a further object of the present invention to provide such a a king pin assembly which does not require manual adjustment, and which is automatically, mechanically adjustable.